The present invention relates to thermoplastic molding compositions which possess desirable resistance to melt dripping.
Thermoplastic molding compositions which are comprised of a thermoplastic polymeric molding resin such as polyethylene terephthalate or polybutylene terephthalate have been known for many years. Such resins have the disadvantage, however, of having the tendency to drip when burning. Any attempt has been made to remedy this problem by the inclusion of asbestos fibers in the thermoplastic molding resin to increase the resistance of the resin to melt dripping. See, for example, commonly-assigned U.S. Pat. No. 3,751,396 (issued to Gall). However, the use of asbestos comprises a health hazard and it would be an advantage to find a non-toxic material which may be used as a substitute for asbestos. Chopped glass fiber has similarly been employed but requires high loading. Polytetrafluoroethylene resin has also been employed in various forms as a melt drip suppressant in molding compositions. See, for example, U.S. Pat. Nos. 3,671,487 (issued to Abolins), 3,294,871 (issued to Schmitt et al), 2,754,223 (issued to Caroselli) and British Pat. No. 946,059. However, the use of polytetrafluoroethylene is expensive and at times not easily incorporated into the molding resin and its use is accordingly commercially unattractive under certain circumstances. It is therefore desirable to provide an alternative method of enhancing the melt drip suppression characteristics of molding resins which is more commercially attractive.